(a) Field of the Invention
The present invention relates to a chain-saw chain sharpening device which is releasably attachable to a portable chain saw to enable routing-type saw chain cutters to be sharpened in situ on the chain-saw guide bar.
(b) Description of the Prior Art
Saw chains with routing-type cutters are very widely used and are characterised by the provision on the leading edge of each cutter tooth of a routing-edge face which is both rearwardly inclined (raked) with respect to the direction of advance of the saw chain and undercut at a predetermined angle.
When in continuous use, the chain of a chain saw requires frequent sharpening to maintain maximum cutting efficiency. Ideally a chain would be re-sharpened two or three times during a working day. Since routing-type cutters cannot be sharpened by holding a grinding surface against the chain while the latter is circulated, the sharpening of router-type chain "in the field" has in the past had to be done by hand using a file. Hand sharpening of a chain is not only very time consuming but, unless expertly done, will result in a crooked cut due to non-uniformity in sharpening of the cutters.
U.S. Pat. No. 4,173,908 discloses a saw chain sharpening fixture for the in-situ sharpening of router-type saw chain cutters. This fixture is arranged to be clamped to the chain-saw guide bar and includes two guides which project laterally on respective sides of the guide bar at the rake angle of the cutters to be sharpened. Each guide is, in turn, used to support a sharpening tool, such as a small-diameter grinding cylinder, which is inserted into the gullet between the depth gauge and tooth of a cutter. In use, the grinding cylinder is powered by an electric drill and is drawn across the routing-edge face of each cutter.
While the sharpening fixture disclosed in U.S. Pat. No. 4,173,908 does expedite sharpening of a saw chain in the field, it also possesses a number of disadvantages, one of the most notable of which is that, owing to the necessarily small diameter of grinding cylinder, only relatively low grinding speeds are obtainable and this limits the quality of the reground faces of the cutters.
It is an object of the present invention to provide an improved chain-saw chain sharpening device.